Predictive Genetic Testing: Do You Really Want To Know Your Future?

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In 1998, when The DNA Files first visited the science and social implications of predictive testing in Predictive Genetic Tests: Do You Really Want to Know Your Future?,
host John Hockenberry said that "A little knowledge is a dangerous
thing." Perhaps the most important idea to take away from this program
is that predictive genetic testing represents just a tiny bit of
knowledge about an extremely complex subject: our genetic makeup.
Scientists had hoped that the complete human genome would quickly lead
us into an age of individualized medicine: Doctors could perform tests
to assess genetic risks for common (and not-so-common) diseases;
determine whether a patient was vulnerable to certain environmental
factors, including cigarette smoke and air pollution; and determine
what drugs would work best for a patient with the fewest harmful side
effects. Although we haven't yet reached the age of individualized
medicine, a growing number of predictive genetic tests can save lives
and influence lifestyle decisions; however, the value of these tests
varies because most have uncertain predictive value.

Many genetic tests are now available to assess genetic risks for
single-gene disorders and multiple-gene disorders. Huntington's disease
is a rare, fatal, single-gene disorder. Patients who inherit the gene
for Huntington's disease will develop it, although the age of onset,
degree and type of clinical symptoms, and the rate of progression are
uncertain. Genetic testing for single-gene disorders is standard in
newborns in many states. For example, children in all 50 states are
tested for phenylketonuria shortly after birth. These children require
a phenylalanine-poor diet in order to prevent mental retardation.

Most newborn screens test for conditions for which treatment is
available. On the other hand, prenatal genetic tests often identify
conditions without therapy or cure. When the results reveal a disorder
or deformity, parents often choose to abort. Many people view this
technology as dangerously close to eugenics, thus scientists,
ethicists, religious leaders, and parents are debating where to draw
the line. Is it ethical for parents to abort a child because the child
will have Tay-Sachs disease or Down syndrome? Is abortion okay if the
child is not going to be the "right" sex?

Multiple-gene disorders, where several mutated genes trigger the
disease, are much more common. Examples include breast cancer,
diabetes, and asthma. Testing for multiple-gene disorders is more
problematic and in most cases can only provide information on a
person's risk of developing a disease, not a definitive diagnosis. Some
risks identified by genetic testing are high; for example, women who
carry certain BRCA1 and BRCA2 mutations are thought to have a 60
percent to 80 percent chance of developing breast cancer in their
lifetimes. However, most breast cancer is not hereditary or genetic. In
the case of BRCA mutations and most other conditions, genes do not
equal destiny. A combination of factors ultimately determines who will
develop cancer, and so far, it remains unclear which ones are important.

Pharmacogenetic tests are a new form of predictive genetic tests that
may see increased clinical application. These tests predict a person's
response to a drug or class of drugs by testing for gene variants such
as those that code for drug-metabolizing enzymes. These tests offer a
means to reduce adverse reactions and increase the efficacy of drug
treatment. For example, a variant in the enzyme
thiopurinemethyltransferase (TPMT) gene increases the risk of
life-threatening reactions to mercaptopurine, a drug used to treat
acute childhood leukemia. When clinicians know the gene is present,
they can adjust the dose.

Rapid advances in research have led to an ever-increasing assortment of
genetic tests. They have also led to a growing public debate. Many
opponents are concerned how the information gained from genetic tests
will be used. They point to cases of discrimination by insurance
companies, employers, and society as a result of genetic testing. They
also express concern about providing information that offers no ability
to act - as in a test for a disease for which there is no cure.
Ultimately, individuals must decide whether they want to pursue genetic
testing, and if they do, what to do with the information gained.

Original Program Description, 1998

If you were destined to live with a disabling disease, would you want
to know now? Would you want to know, for example, that because your
family carries a particular gene you are likely to contract
Huntington's disease, an incurable condition that eventually devastates
both mind and body? It's the kind of question more and more of us are
having to face. This program offers an overview of predictive genetic
testing. You'll learn which diseases it currently targets, the testing
techniques, the reliability of those tests, and, most important of all,
what is achievable once the results are obtained.

In only a very small percentage of diseases is the gene the ruler - the
unequivocal dictator that determines the onset of the condition.
Nonetheless, predictive genetic tests are becoming increasingly
available. One company offers a test for the gene that identifies a
possible predisposition for breast cancer. And researchers are coming
up with ways to look for genes related to cardiovascular disease,
asthma, osteoporosis, obesity, depression, stroke, and pulmonary
disease. If scientists identify these genes, and companies come up with
tests to identify them in you, what will you do with that information?
Maybe you'll find it helpful in preparing for the likely debilitation
of yourself or a family member. If you're lucky, some treatment will be
available, or a lifestyle change might make a difference in your
prognosis.

Often, however, there is absolutely nothing that can be done to treat
the disease, and having the genetic information creates a tremendous
psychological burden for entire families.

This program introduces us to people whose family history has compelled
them to decide whether to undergo genetic testing. You'll hear,
first-hand, how families have dealt with Huntington's disease and
Alzheimer's. And you'll find out how tests for colon cancer and breast
cancer are viewed by health care providers, by scientists, and by
representatives of the companies that are busy developing genetic tests.

The issues are difficult - and pressing, as the pace of genetic
research advances rapidly. In the near future, a predisposition for
many more diseases will be identifiable through genetic testing. Will
treatment and cure keep up with prediction? Do you really want to know
your destiny?